A printed circuit board system, as referred to herein, includes a printed circuit board or the like to which are mounted a plurality of electrical components such as integrated circuit packages, switches, connectors, resistors, capacitors, etc. The electrical components usually are mounted to one side of the printed circuit board with the leads thereof connected to leads of other components by circuit traces on the substrate of the printed circuit board.
The process of designing a printed circuit board system has often been time consuming and costly. The system may call for numerous integrated circuit packages and other electrical devices each having numerous leads that require connection to leads of other components mounted on the printed circuit board and/or other leads of the same device. The design task is complicated by the often limited real estate on the board for the electrical components and circuit traces and by the need to route circuit traces so that they do not cross other circuit traces on the same surface of the board substrate unless their electrical connection is intended. Considerable skill and effort often are needed strategically to locate the system components and circuit traces on the board substrate.
To facilitate or enable the physical layout of some printed circuit board systems, circuit traces have been provided on both sides of the board substrate with plated through holes electrically connecting circuit traces on one side of the board substrate to circuit traces on the other side of the board substrate. More complex systems have necessitated the use of more costly multi-layer printed circuit boards. In multi-layer printed circuit boards, plated through holes are used to connect circuit traces at one layer in the board to circuit traces at one or more layers as is shown, for example, in U.S. Pat. No. 3,923,359. Also, the added board layers do not result in any corresponding increase in real estate for active and passive electrical components. Jumper wires also have been used to move one interconnection path across another in a printed circuit board system.
In the above referenced copending application Ser. No. 792,482, a programmable integrated crosspoint switch is disclosed along with various applications thereof having certain advantages and benefits. As therein indicated, the programmable integrated crosspoint switch may be used to facilitate the manufacture of a printed circuit board system by avoiding or minimizing the need for plated through holes, jumper wires, etc. to move one interconnection path across another interconnection path at a common side or circuit plane of the printed circuit board. The programmable integrated crosspoint switch includes a matrix of first and second pluralities of electrically conductive paths and selectively permanently and affirmatively programmable means for completing passive conductive circuit paths between one or more of the conductive paths of such first and second pluralities thereof. The programmable integrated crosspoint switch electronic programmability characteristic enables economical volume manufacture and end user programming for any desired application. Moreover, its relatively small size, in relation to the programmed and programmable devices disclosed in U.S. Pat. No. 4,588,239, No. 4,557,540 and No. 4,609,241, is important to high density, limited real estate applications. The socket devices shown in these patents had a relatively large footprint and generally were not practical for high density board applications; the devices took up too much real estate which usually is limited to provide a small overall package size for the printed circuit board system.
Presently the design of printed circuit board systems is moving in the direction of surface mount technology wherein the electrical components are mounted to a surface of the printed circuit board rather than through the printed circuit board. Such surface mounting usually is effected without the need for plated through holes that had been required to accommodate the solder tails of non-surface mount components. In those systems employing surface mount technology, plated through holes and consequently multi-layer printed circuit boards are counter-productive, although some use thereof has been found desirable when mounting input/output connection devices such as headers to the printed circuit board for the reasons discussed in copending application Ser. No. 747,343, filed June 21, 1985.
By way of a specific representative example, the casing of an electronic apparatus such as a calculator may double as the substrate of a printed circuit board to reduce size, weight and number of parts. That is, circuit traces may be printed onto the inside surface of the casing and a surface mount technique employed to mount electrical components to the inside surface of the casing. Obviously, this application precludes the use of plated through holes and circuit traces on the outside surface of the casing. Accordingly, the designer is limited to printed circuit interconnections at a single surface or circuit plane and, accordingly, to a correspondingly limited degree of circuit complexity in relation to the interconnection potential of multi-plane circuit interconnection system.